The present invention relates generally to apparatus having mechanisms which are subject to wear and/or sluggish response from factors such as age, friction, or accumulations of residue in the moving parts, and to systems for diagnosing the existence of such wear and/or sluggish response so that appropriate servicing and maintenance may be directed to the affected parts. The invention particularly relates to the application of such diagnostic systems to amusement machines having rotating reel assemblies, such as coin operated slot machines of the type found in Monte Carlo, Reno and other internationally known gaming resorts.